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Honeycomb Carbon: A Review of Graphene

Electrolytes and interphases in Li-ion batteries and beyond.

To realize graphene-based electronics, various types of graphene are required; thus, modulation of its electrical properties is of great importance. Theoretic studies show that intentional doping is a promising route for this goal, and the doped graphene might promise fascinating properties and widespread applications. However, there is no experimental example and electrical testing of the substitutionally doped graphene up to date. Here, we synthesize the N-doped graphene by a chemical vapor deposition (CVD) method. We find that most of them are few-layer graphene, although single-layer graphene can be occasionally detected. As doping accompanies with the recombination of carbon atoms into graphene in the CVD process, N atoms can be substitutionally doped into the graphene lattice, which is hard to realize by other synthetic methods. Electrical measurements show that the N-doped graphene exhibits an n-type behavior, indicating substitutional doping can effectively modulate the electrical properties of graphene. Our finding provides a new experimental instance of graphene and would promote the research and applications of graphene.

Synthesis of N-Doped Graphene by Chemical Vapor Deposition and Its Electrical Properties

Graphitic carbon nitride, g-C3N4, can be made by polymerization of cyanamide, dicyandiamide or melamine. Depending on reaction conditions, different materials with different degrees of condensation, properties and reactivities are obtained. The firstly formed polymeric C3N4 structure, melon, with pendant amino groups, is a highly ordered polymer. Further reaction leads to more condensed and less defective C3N4 species, based on tri-s-triazine (C6N7) units as elementary building blocks. High resolution transmission electron microscopy proves the extended two-dimensional character of the condensation motif. Due to the polymerization-type synthesis from a liquid precursor, a variety of material nanostructures such as nanoparticles or mesoporous powders can be accessed. Those nanostructures also allow fine tuning of properties, the ability for intercalation, as well as the possibility to give surface-rich materials for heterogeneous reactions. Due to the special semiconductor properties of carbon nitrides, they show unexpected catalytic activity for a variety of reactions, such as for the activation of benzene, trimerization reactions, and also the activation of carbon dioxide. Model calculations are presented to explain this unusual case of heterogeneous, metal-free catalysis. Carbon nitride can also act as a heterogeneous reactant, and a new family of metal nitride nanostructures can be accessed from the corresponding oxides.

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Graphitic carbon nitride materials: variation of structure and morphology and their use as metal-free catalysts

Polymeric graphitic carbon nitride materials (for simplicity: g-C(3)N(4)) have attracted much attention in recent years because of their similarity to graphene. They are composed of C, N, and some minor H content only. In contrast to graphenes, g-C(3)N(4) is a medium-bandgap semiconductor and in that role an effective photocatalyst and chemical catalyst for a broad variety of reactions. In this Review, we describe the "polymer chemistry" of this structure, how band positions and bandgap can be varied by doping and copolymerization, and how the organic solid can be textured to make it an effective heterogenous catalyst. g-C(3)N(4) and its modifications have a high thermal and chemical stability and can catalyze a number of "dream reactions", such as photochemical splitting of water, mild and selective oxidation reactions, and--as a coactive catalytic support--superactive hydrogenation reactions. As carbon nitride is metal-free as such, it also tolerates functional groups and is therefore suited for multipurpose applications in biomass conversion and sustainable chemistry.

Polymeric Graphitic Carbon Nitride as a Heterogeneous Organocatalyst: From Photochemistry to Multipurpose Catalysis to Sustainable Chemistry

Near IR Photodiodes with Tunable Absorption Edge Based on Ge1-y Sny Alloys Integrated on Silicon

Thermal expansivity ofGe1−ySnyalloys

Chemical precursors are used to grow crystalline Ge–C materials with unusual morphologies that depend on the molecular design of the precursor and the C concentration. Ge–C nanorods with overall C content of about 13–15 at. % and lattice constants close to that of pure Si grew very rapidly from the surface of a 40 nm Ge–C epitaxial film. Coherent carbide islands are formed after epitaxial growth of 20 nm Ge1−xCx (x=9 at. %) on (100)Si. Lower reaction temperatures resulted in extremely low growth rate of epitaxial Ge1−xCx (x=3–5 at. %) heterostructures with very flat surfaces implying two-dimensional layer-by-layer growth. The use of precursor chemistry as reported here to control morphology and composition in the Ge–C system may provide a simple and reliable synthetic route to a new family of Si-based heterostructures.

Morphological control and structural characteristics of crystalline Ge–C systems: Carbide nanorods, quantum dots, and epitaxial heterostructures

The dielectric functions of GeSn and GeSiSn alloys were measured in the 1–6 eV energy range using spectroscopic ellipsometry. The contributions from the E 1 , E 1  + Δ 1 , E 0 ′, E 2 , and E 1 ′ critical points in the joint density of electronic states were enhanced by computing numerical second derivatives of the measured dielectric function, and the resulting lineshapes were fitted with model expressions from which the critical point energies, amplitudes, broadenings, and phases were determined. A detailed analysis of the compositional dependence of the different transition energies is presented. By describing this dependence in terms of quadratic polynomials, the bowing parameter (quadratic coefficient) for each transition is determined. It is shown that the bowing parameters in the ternary alloy follow a distinct chemical trend, in which the ternary is well described in terms of bowing parameters for the underlying binary alloys, and these bowing parameters increase as a function of the size and electronegativity mismatch of the alloy constituents.

John Kouvetakis

Papers

Near IR Photodiodes with Tunable Absorption Edge Based on Ge1-y Sny Alloys Integrated on Silicon

Thermal expansivity ofGe1−ySnyalloys

Morphological control and structural characteristics of crystalline Ge–C systems: Carbide nanorods, quantum dots, and epitaxial heterostructures

Compositional dependence of optical interband transition energies in GeSn and GeSiSn alloys

ZrB2(0001)上,GaN(0001)ヘテロエピタクシーの第一原理研究